Quote:
Originally Posted by Rallye469
I think you'll find that the carb on your 307 will be very restrictive on your
425. You'll want to look at 750 cfm probably.
I've never run an OB4 intake but, is there no way to grind off a bit of it
to fit your HEI back on?
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*****Please do NOT try to grind the manifold to clear the HEI. You will end up inside that runner*****
Also, you will NEED to change distributor gears to run an HEI on the 425. The 330, and 425 gear is .060 shorter, and will jam against the block, and possibly ruin the gear, cam, and block.
The q-jet is not restrictive, the secondaries open for only what the engine wants. Most q-jets (AND ALL that came on 425's) were rated at the same "750" number (actualy, I think that is more like 735 cfm). I would be more concerned with fuel metering with factory jets, and the computer shyt. You may want to look into an earlier q-jet.
It would look more like a factory install (not to mention run better, and use FAR less fuel) with the q-jet, but you may need to have the O4B opened up to match the secondary throttle plate size. Most O4B manifolds did not have the spread bore pattern cut, but they can be modified for it.
Nice engine, 39 degree lifter bank (although with .921 lifters), cool manifold (check underside for cracks, and make sure to block your heat risers when you run this one), water pumps interchange, DO NOT try the 307 starter, it will let you down. Use a 425 starter. You may need a spacer betwen the alt, and power stering brackets due to deck height of engine. Factory engine mounts for the Caddy/307 will bolt right up to the 425. Get the shortblock rebuilt, and have some fun!!!
GOOD LUCK!
Jim in Phx.